Type I Diabetes is a devastating life-long disease affecting children and young adults which results from thedestruction of insulin-producing beta (beta) cells of the islets of Langerhans in the pancreas. The disturbance in glucose metabolism causes many life-threatening complications despite the availability of exogenous insulin therapy. The recent success with human islet transplantation resulting in an 80% graft survival rate at one year has sparked enthusiasm that this therapy will restore long-term euglycemia to many patients with diabetes. This success is dependent on transplantation of a large islet mass which usually involves multiple sequential islet transplants. It is generally believed that the need for a substantial mass of islets is necessary because only a fraction of the transplanted islets survive following transplantation. Recent advances in cell biology highlighting the critical role of ambient oxygen as a molecular signal which influences cell phenotype, gene expression and function may have critical importance for optimizing islet cell function and viability for transplant. Maintenance of a "normal" range of ambient oxygen minimizes cellular oxidative stress and preserves cellular integrity. In mammalian organs, there is a wide range of oxygen concentrations such that "normoxia" for different cell types is variable. "Hypoxic" conditions are known to significantly influence cellular signaling and oxidative stress responses. Recent published work from our research team demonstrates that "hyperoxic" conditions also significantly influence cellular signaling, gene expression, phenotype and production of reactive oxygen species. Given the extreme vulnerability of pancreatic islets to oxidative stress, we suspect that current clinical approaches which involve dramatic fluctuations in ambient oxygen from "hyperoxic" to"hypoxic" conditions adversely influence islet cell function and viability. The proof of concept that hypoxia preconditioning initiates a cytoprotection cascade which reduces redox stress has been established for a variety of (nonpancreatic) cell types and tissues. This proposal will test the hypothesis that hypoxia preconditioning to readjust the"normoxia" set point of pancreatic islets to their hypoxic microenvironment prior to transplant will initiate cytoprotective cellular signaling pathways, resulting in successful islet transplantation with decreased islet mass. In preliminary data we show that improved viability and recovery of islets occur after hypoxia pre-conditioning. Specific Aim I: To examine the effects of ambient oxygen over time on islet cell viability and recovery after culture. The influence of ambient oxygen on islet cell viability, morphology and recovery after culture will be determined using in vitro assays and microscopy. Specific Aim II: To determine the effect of oxygen pre-conditioning on islet cell function in vivo. The effect of oxygen pre-conditioning on islet viability and function in vivo will be determined using fluorescence microscopy and the marginal mass model of islet transplantation.